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How to reduce PDF size for email and upload limits
Short answer
- Large PDFs are almost always scans or documents full of photos. A PDF that is mostly text rarely shrinks much with compression.
- Work in this order: remove pages you do not need, try Safe compression, then use Strong compression only if the file is still too big.
- Strong compression turns each page into an image, so text search, links and form fields are lost. Keep the original file.
Common size limits you may run into
Gmail accepts attachments up to 25 MB per message and Outlook.com up to 20 MB. Because email encodes attachments, a file close to the limit can still be rejected, so aim a little below it. Job application systems, university portals and government forms vary widely; many cap a single file somewhere between 2 and 10 MB. The limit stated on the upload page is the one that counts.
Why is this PDF so big?
File size depends far more on the images inside a PDF than on its page count. A document photographed with a phone, or scanned in colour at high resolution, can easily take several megabytes per page. A report exported straight from Word or Google Docs is often under 1 MB even at dozens of pages.
| Document type | Most effective fix | Watch out for |
|---|---|---|
| Phone photos or scans | Strong compression, or rescanning at a lower resolution | Small print becoming blurry |
| Reports with many photos | Safe compression first, Strong if needed | Visible loss of photo quality |
| Mostly text | Delete unneeded pages, or split the file | Compression may change very little |
| Already-compressed PDFs | Delete pages or send in parts | Compressing again can make the file larger |
The order to try
- Remove pages you do not need. Covers, blank pages and duplicate scans add size for nothing. Delete PDF Pages removes them without touching the quality of the pages you keep.
- Try Safe compression. In Compress PDF, Safe compression keeps the document’s text and structure and only reorganises how it is stored. The saving can be small or zero, but nothing is lost.
- If it is still too large, choose Strong compression. Strong rebuilds every page as an image, which can shrink scans considerably. You can enter a target size in KB or MB, but reaching it exactly is not guaranteed; if it is missed, the tool gives you the smallest result it found.
- As a last resort, split the file. If the form accepts several attachments, Split PDF keeps every page at full quality and simply spreads them across files.
The compression tool analyses the document first and recommends Safe or Strong based on whether it looks like a scan, text-heavy, mixed or already optimised. On phones, files from 20 MiB trigger a warning and files of 50 MiB or more are blocked to avoid running out of memory, so very large files are better handled on a computer.
If you can rescan the paper
When the paper original is still to hand, changing the scan settings is the cleanest fix. For ordinary documents, greyscale or black-and-white instead of colour, and around 150 dpi instead of 300 dpi, is usually enough to read on screen. Documents with signatures, stamps or very small print may need more, so check what the recipient requires.
Check before you send
- Open the compressed file and zoom in on every page to confirm the smallest text, numbers and signatures are still legible.
- Page order and orientation are correct. If pages are sideways or shuffled, see fixing a scanned PDF’s page order and orientation.
- The file name follows any naming rule the recipient asked for.
- You kept the original, uncompressed PDF.